Environmental factors associated with juvenile and adult Patagonian toothfish (Dissostichus eleginoides) distribution around South Georgia and the South Sandwich Islands

Understanding the environmental factors driving the distribution of harvested fish species is essential for effective fisheries management, particularly in a changing climate. We investigated the spatial distribution of Patagonian toothfish (Dissostichus eleginoides) around South Georgia and the South Sandwich Islands, located in the rapidly changing southwest Atlantic sector of the Southern Ocean, where a commercial longline fishery for this species operates. Using scientific demersal trawl survey data, we examined environmental factors linked to the distribution of Patagonian toothfish at South Georgia, focusing on temperature and ontogenetic shifts across different developmental stages. Distribution models, informed by environmental covariates, were constructed for six size-classes (26 cm to 66 cm total length), representing approximate annual age groups. Depth and temperature were strongly associated with distribution, with larger size-classes occupying progressively deeper habitats. Temperature relationships were evident across all size-classes, but strongest for the three smallest, with higher abundances predicted at locations where annual mean sea surface temperature exceeded 1.8°C. This suggests that spatial distribution patterns during early life stages correspond to surface temperature conditions and that this relationship persists through early growth. Adult distributions across South Georgia and the South Sandwich Islands were explored using longline fishery data. At the South Sandwich Islands, catch-per-unit-effort declined to near zero at seafloor temperatures of 0.3°C or below, coinciding with catches largely restricted to the northern part of the island chain. Overall, the results highlight strong associations between depth, temperature and Patagonian toothfish distribution, providing new insight into the timing of ontogenetic shifts and the environmental thresholds shaping spatial patterns. Understanding life stage-specific environmental sensitivities is important for improving forecasts of distributional shifts and informing fisheries management under climate change.